This invention relates to metal sheet piling. More especially, but not exclusively, the invention relates to steel sheet piling.
Steel sheet piles are used in general and marine engineering as permanent structures inter alia for retaining walls, basements, underground car parks, pumping stations, bridge abutments and marine structures. These are only examples of such structures.
Conventional sheet piles include those known as Larssen or LX sheet piles which are of generally xe2x80x9cUxe2x80x9d shape and comprise a wall section comprising a pan defined by a central flange flanked by outwardly inclined side walls along the free edges of which are integrally formed interlocks. These interlocks (also known as clutches) typically comprise a locking toe of generally triangular cross-section which stands proud of a lip which extends along each side edge of the pile, the lip lying generally normal to the adjoining pile surface. The space between the toe and the lip defines a recess for receiving a locking toe of an adjoining pile. The lip defines the bottom wall of this recess.
Other known sheet piles include Frodingham piles which are of generally xe2x80x9cZxe2x80x9d profile and typically comprise a wall section including an inclined central web flanked by outwardly extending flanges along the free edges of which are formed interlocks.
Many variations and combinations of the sheet piles and clutches described are possible.
Steel sheet piles are conventionally produced by hot rolling. Typically, the required profile is produced by subjecting re-heated steel slab, bar or other suitable section to sequential rolling. The clutches are formed integrally during the course of this hot rolling.
A perceived disadvantage of hot rolling is that it is limiting as to the size and profile of sheet pile which can be produced using any given set of rolls.
Cold forming of clutch sections has previously been proposed. However, only relatively simple shaped clutches can be produced by cold forming. An example of such a clutch section is to be found in GB-A-1343203. This document discloses a pile which comprises an elongate web to the longitudinal edges of which are secured elongate flanges whose longitudinal edges are bent back towards the general plane of the web by cold roll bending to form hook-shaped clutch sections which are adapted to interlock with a similar clutch section of an adjacent pile. A similar sheet pile is disclosed in U.S. Pat. No. 2,093,208.
Sheet piles which comprise wall sections profiled by cold stamping and pressing from sheet metal blanks of the required length and width are disclosed in EP-A-164296. The sheet edges of adjoining piles are joined by connecting elements produced by cold stamping or laminating using bolts, rivets or welding.
Cold formed clutches have frequently been found not to provide the required interlock between adjoining sheet piles in service.
One object of the present invention is to provide a metal sheet pile which overcomes or at least alleviates many of the disadvantages to be found in existing sheet piles. Another object of this invention is to provide a method of making such improved metal sheet piles.
According to the present invention in one aspect, there is provided a sheet pile which comprises a cold formed wall section of sheet metal to the longitudinally extending side-edges of which are secured hot formed clutch sections.
The term xe2x80x9ccold formedxe2x80x9d when used in relation to steel or other metallic material means that the material has been subjected to a forming operation at a temperature below the hot forming temperature of the material; the term xe2x80x9chot formedxe2x80x9d applies when the material has been subjected to a forming operation at a temperature at or above the hot forming temperature. In the case of hot forming, the deformation processes proceed at a rate which does not exceed the rate of the recovery processes which are themselves temperature dependent, being faster at higher temperatures; the converse is true for cold working or forming, where the recovery processes cannot keep pace with the deformation processes.
As mentioned above, the hot formed metal clutch sections are formed separately and not integrally with the steel sheet. The hot formed clutch sections may be produced by, for example, hot rolling or extrusion and are preferably welded to the side edges of the pan or web by, for example, laser, submerged arc or resistance welding. Other welding techniques may be employed. Alternatively, the clutch sections may be secured to the wall sections by, for example, bolts, rivets, adhesive or prestressed fastenings. The clutch sections are preferably produced from steel. Alternatively, the clutch sections may be produced from a non-ferrous material having the required physical properties.
Cold forming of the wall section from metal plate may be effected in a press, or by passing plate between or around cold bending rolls. Other cold forming processes may be adopted.
The gauge of the pan or web profile of a wall section and the clutch sections may differ one from the other. Also, for steel piles, the grade of steel employed for the wall sections may be the same or may differ from that employed for one or both clutch sections. Furthermore, the length of each clutch section may be the same as or shorter than the wall section side edge to which it is to be secured. With clutch sections whose length is less than the adjoining wall section side edge, more than one clutch section may be provided, the overall length of the clutch sections being equal to or less than the length of the respective wall section side edge. The clutch section profile positioned along one side edge of a wall section may differ from the profile of the clutch section positioned along the other side edge of the wall section. Such a pile may act, for example, as a transition pile.
In another aspect, there is provided a method of producing a metal sheet pile which comprises subjecting a metal plate to cold forming to produce in that metal plate the required wall profile of the finished sheet pile, subjecting separate lengths of metal to a hot forming operation to produce in those lengths the required clutch profile, and securing to one or each longitudinal edge of the cold formed metal wall section a hot formed clutch.
The metal plate to be cold formed may be cut to length and width prior to cold forming. The width may be achieved by rolling. Alternatively, plate of the required width and length may be slit or cut from larger plate. Cold forming may, for example, be effected in a press or by passage of the plate through or around a cold bending roll or rolls. Other cold forming techniques may be employed.
Steel for a clutch section may be in slab, rod or like form, or may be cut or slit from larger sheets of plate. Hot forming of the clutch sections may be effected, for example, by hot rolling or extrusion.
Conventional structural steels in alloy or non-alloy grades may be used for the cold formed wall sections. Such steels may also be used for the clutch sections.
One advantage of the present invention is that the thickness and/or geometry of the section is infinitely variable, Also, the overall depth of section, width of flanges and angle of bend can be varied to provide a finished product with specified geometry or with given engineering properties which may include inertia, section modulus, section area or unit width. It is believed that sheet piles in accordance with the invention will exhibit improvements in strength to weight ratio, measured in terms of section modulus per metre width to weight per square metre of product, when compared to conventional hot rolled sheet piles of equivalent strength.
With sheet piles in accordance with the invention, it is possible for the length or height of some sheet piles in an assembly of such piles to be curtailed, the longer sheet piles acting as primary piling and those whose length or height is curtailed acting as secondary piling. The length of curtailed secondary piles may be 40% or more of the length of the primary piles.